Conventionally, in a ball screw including a threaded shaft and a nut which is in threaded engagement with the threaded shaft and relatively rotatable, point contact or surface contact occurs during relative rotation. Therefore, a cooling means (heat exchanger) is sometimes provided at the nut.
As such a cooling means, a cooling passage arranged in the nut of the ball screw for circulating the coolant is disclosed (see e.g., Patent Literature (hereinafter referred to as PTL) 1). The above document also discloses a cooling technique of a nut in the ball screw adopting a double-nut preload type. The above document also discloses a configuration having a spacer interposed between two nuts and an O-ring attached to a mating surface of each of the two nuts. Then, the two nuts are cooled by flowing the coolant through the through-holes formed in the nuts in axial directions thereof.